MMI G2 Issue

Hi
Have an A6 (C6) with the G2 MMI. After the car sitting idle for a year had to jump start. This seems to have knocked out the MMI. Nothing lights up or responds.
Took it to Audi dealer who ran various diagnostics. Wanted £300+ for work, but as they could not diagnose the problem didn't charge me. What are my options?
Feel free to ask questions as I have been quite vague.
Look forward to hearing your thoughts.